X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=drivers%2Ftty%2Ftty_buffer.c;h=c043136fbe5198cf0a7a8704254fc28763ecd0b9;hb=1a7b0ecbbc1219895f48934ff5549a3594db3480;hp=069640e5b9c0eb95fca133525d9beaaf75391770;hpb=809850b7a5fcc0a96d023e1171a7944c60fd5a71;p=firefly-linux-kernel-4.4.55.git diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 069640e5b9c0..c043136fbe51 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -22,6 +22,77 @@ #define MIN_TTYB_SIZE 256 #define TTYB_ALIGN_MASK 255 +/* + * Byte threshold to limit memory consumption for flip buffers. + * The actual memory limit is > 2x this amount. + */ +#define TTYB_MEM_LIMIT 65536 + +/* + * We default to dicing tty buffer allocations to this many characters + * in order to avoid multiple page allocations. We know the size of + * tty_buffer itself but it must also be taken into account that the + * the buffer is 256 byte aligned. See tty_buffer_find for the allocation + * logic this must match + */ + +#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF) + + +/** + * tty_buffer_lock_exclusive - gain exclusive access to buffer + * tty_buffer_unlock_exclusive - release exclusive access + * + * @port - tty_port owning the flip buffer + * + * Guarantees safe use of the line discipline's receive_buf() method by + * excluding the buffer work and any pending flush from using the flip + * buffer. Data can continue to be added concurrently to the flip buffer + * from the driver side. + * + * On release, the buffer work is restarted if there is data in the + * flip buffer + */ + +void tty_buffer_lock_exclusive(struct tty_port *port) +{ + struct tty_bufhead *buf = &port->buf; + + atomic_inc(&buf->priority); + mutex_lock(&buf->lock); +} + +void tty_buffer_unlock_exclusive(struct tty_port *port) +{ + struct tty_bufhead *buf = &port->buf; + int restart; + + restart = buf->head->commit != buf->head->read; + + atomic_dec(&buf->priority); + mutex_unlock(&buf->lock); + if (restart) + queue_work(system_unbound_wq, &buf->work); +} + +/** + * tty_buffer_space_avail - return unused buffer space + * @port - tty_port owning the flip buffer + * + * Returns the # of bytes which can be written by the driver without + * reaching the buffer limit. + * + * Note: this does not guarantee that memory is available to write + * the returned # of bytes (use tty_prepare_flip_string_xxx() to + * pre-allocate if memory guarantee is required). + */ + +int tty_buffer_space_avail(struct tty_port *port) +{ + int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used); + return max(space, 0); +} + static void tty_buffer_reset(struct tty_buffer *p, size_t size) { p->used = 0; @@ -37,8 +108,6 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size) * * Remove all the buffers pending on a tty whether queued with data * or in the free ring. Must be called when the tty is no longer in use - * - * Locking: none */ void tty_buffer_free_all(struct tty_port *port) @@ -49,14 +118,18 @@ void tty_buffer_free_all(struct tty_port *port) while ((p = buf->head) != NULL) { buf->head = p->next; - kfree(p); + if (p->size > 0) + kfree(p); } llist = llist_del_all(&buf->free); llist_for_each_entry_safe(p, next, llist, free) kfree(p); - buf->tail = NULL; - buf->memory_used = 0; + tty_buffer_reset(&buf->sentinel, 0); + buf->head = &buf->sentinel; + buf->tail = &buf->sentinel; + + atomic_set(&buf->memory_used, 0); } /** @@ -89,7 +162,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) /* Should possibly check if this fails for the largest buffer we have queued and recycle that ? */ - if (port->buf.memory_used + size > 65536) + if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT) return NULL; p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC); if (p == NULL) @@ -97,7 +170,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) found: tty_buffer_reset(p, size); - port->buf.memory_used += size; + atomic_add(size, &port->buf.memory_used); return p; } @@ -115,72 +188,42 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b) struct tty_bufhead *buf = &port->buf; /* Dumb strategy for now - should keep some stats */ - buf->memory_used -= b->size; - WARN_ON(buf->memory_used < 0); + WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0); if (b->size > MIN_TTYB_SIZE) kfree(b); - else + else if (b->size > 0) llist_add(&b->free, &buf->free); } /** - * __tty_buffer_flush - flush full tty buffers + * tty_buffer_flush - flush full tty buffers * @tty: tty to flush * - * flush all the buffers containing receive data. Caller must - * hold the buffer lock and must have ensured no parallel flush to - * ldisc is running. + * flush all the buffers containing receive data. If the buffer is + * being processed by flush_to_ldisc then we defer the processing + * to that function * - * Locking: Caller must hold tty->buf.lock + * Locking: takes buffer lock to ensure single-threaded flip buffer + * 'consumer' */ -static void __tty_buffer_flush(struct tty_port *port) +void tty_buffer_flush(struct tty_struct *tty) { + struct tty_port *port = tty->port; struct tty_bufhead *buf = &port->buf; struct tty_buffer *next; - if (unlikely(buf->head == NULL)) - return; + atomic_inc(&buf->priority); + + mutex_lock(&buf->lock); while ((next = buf->head->next) != NULL) { tty_buffer_free(port, buf->head); buf->head = next; } - WARN_ON(buf->head != buf->tail); buf->head->read = buf->head->commit; -} - -/** - * tty_buffer_flush - flush full tty buffers - * @tty: tty to flush - * - * flush all the buffers containing receive data. If the buffer is - * being processed by flush_to_ldisc then we defer the processing - * to that function - * - * Locking: none - */ - -void tty_buffer_flush(struct tty_struct *tty) -{ - struct tty_port *port = tty->port; - struct tty_bufhead *buf = &port->buf; - unsigned long flags; - - spin_lock_irqsave(&buf->lock, flags); - - /* If the data is being pushed to the tty layer then we can't - process it here. Instead set a flag and the flush_to_ldisc - path will process the flush request before it exits */ - if (test_bit(TTYP_FLUSHING, &port->iflags)) { - set_bit(TTYP_FLUSHPENDING, &port->iflags); - spin_unlock_irqrestore(&buf->lock, flags); - wait_event(tty->read_wait, - test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0); - return; - } else - __tty_buffer_flush(port); - spin_unlock_irqrestore(&buf->lock, flags); + atomic_dec(&buf->priority); + mutex_unlock(&buf->lock); } /** @@ -190,38 +233,26 @@ void tty_buffer_flush(struct tty_struct *tty) * * Make at least size bytes of linear space available for the tty * buffer. If we fail return the size we managed to find. - * - * Locking: Takes port->buf.lock */ int tty_buffer_request_room(struct tty_port *port, size_t size) { struct tty_bufhead *buf = &port->buf; struct tty_buffer *b, *n; int left; - unsigned long flags; - spin_lock_irqsave(&buf->lock, flags); - /* OPTIMISATION: We could keep a per tty "zero" sized buffer to - remove this conditional if its worth it. This would be invisible - to the callers */ + b = buf->tail; - if (b != NULL) - left = b->size - b->used; - else - left = 0; + left = b->size - b->used; if (left < size) { /* This is the slow path - looking for new buffers to use */ if ((n = tty_buffer_alloc(port, size)) != NULL) { - if (b != NULL) { - b->next = n; - b->commit = b->used; - } else - buf->head = n; buf->tail = n; + b->commit = b->used; + smp_mb(); + b->next = n; } else size = left; } - spin_unlock_irqrestore(&buf->lock, flags); return size; } EXPORT_SYMBOL_GPL(tty_buffer_request_room); @@ -235,8 +266,6 @@ EXPORT_SYMBOL_GPL(tty_buffer_request_room); * * Queue a series of bytes to the tty buffering. All the characters * passed are marked with the supplied flag. Returns the number added. - * - * Locking: Called functions may take port->buf.lock */ int tty_insert_flip_string_fixed_flag(struct tty_port *port, @@ -247,10 +276,8 @@ int tty_insert_flip_string_fixed_flag(struct tty_port *port, int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); int space = tty_buffer_request_room(port, goal); struct tty_buffer *tb = port->buf.tail; - /* If there is no space then tb may be NULL */ - if (unlikely(space == 0)) { + if (unlikely(space == 0)) break; - } memcpy(char_buf_ptr(tb, tb->used), chars, space); memset(flag_buf_ptr(tb, tb->used), flag, space); tb->used += space; @@ -273,8 +300,6 @@ EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag); * Queue a series of bytes to the tty buffering. For each character * the flags array indicates the status of the character. Returns the * number added. - * - * Locking: Called functions may take port->buf.lock */ int tty_insert_flip_string_flags(struct tty_port *port, @@ -285,10 +310,8 @@ int tty_insert_flip_string_flags(struct tty_port *port, int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); int space = tty_buffer_request_room(port, goal); struct tty_buffer *tb = port->buf.tail; - /* If there is no space then tb may be NULL */ - if (unlikely(space == 0)) { + if (unlikely(space == 0)) break; - } memcpy(char_buf_ptr(tb, tb->used), chars, space); memcpy(flag_buf_ptr(tb, tb->used), flags, space); tb->used += space; @@ -311,20 +334,14 @@ EXPORT_SYMBOL(tty_insert_flip_string_flags); * processing by the line discipline. * Note that this function can only be used when the low_latency flag * is unset. Otherwise the workqueue won't be flushed. - * - * Locking: Takes port->buf.lock */ void tty_schedule_flip(struct tty_port *port) { struct tty_bufhead *buf = &port->buf; - unsigned long flags; WARN_ON(port->low_latency); - spin_lock_irqsave(&buf->lock, flags); - if (buf->tail != NULL) - buf->tail->commit = buf->tail->used; - spin_unlock_irqrestore(&buf->lock, flags); + buf->tail->commit = buf->tail->used; schedule_work(&buf->work); } EXPORT_SYMBOL(tty_schedule_flip); @@ -340,8 +357,6 @@ EXPORT_SYMBOL(tty_schedule_flip); * accounted for as ready for normal characters. This is used for drivers * that need their own block copy routines into the buffer. There is no * guarantee the buffer is a DMA target! - * - * Locking: May call functions taking port->buf.lock */ int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars, @@ -370,8 +385,6 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string); * accounted for as ready for characters. This is used for drivers * that need their own block copy routines into the buffer. There is no * guarantee the buffer is a DMA target! - * - * Locking: May call functions taking port->buf.lock */ int tty_prepare_flip_string_flags(struct tty_port *port, @@ -414,9 +427,10 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count) * This routine is called out of the software interrupt to flush data * from the buffer chain to the line discipline. * - * Locking: holds tty->buf.lock to guard buffer list. Drops the lock - * while invoking the line discipline receive_buf method. The - * receive_buf method is single threaded for each tty instance. + * The receive_buf method is single threaded for each tty instance. + * + * Locking: takes buffer lock to ensure single-threaded flip buffer + * 'consumer' */ static void flush_to_ldisc(struct work_struct *work) @@ -424,7 +438,6 @@ static void flush_to_ldisc(struct work_struct *work) struct tty_port *port = container_of(work, struct tty_port, buf.work); struct tty_bufhead *buf = &port->buf; struct tty_struct *tty; - unsigned long flags; struct tty_ldisc *disc; tty = port->itty; @@ -435,42 +448,31 @@ static void flush_to_ldisc(struct work_struct *work) if (disc == NULL) return; - spin_lock_irqsave(&buf->lock, flags); - - if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) { - struct tty_buffer *head; - while ((head = buf->head) != NULL) { - int count; - - count = head->commit - head->read; - if (!count) { - if (head->next == NULL) - break; - buf->head = head->next; - tty_buffer_free(port, head); - continue; - } - spin_unlock_irqrestore(&buf->lock, flags); - - count = receive_buf(tty, head, count); - - spin_lock_irqsave(&buf->lock, flags); - /* Ldisc or user is trying to flush the buffers. - We may have a deferred request to flush the - input buffer, if so pull the chain under the lock - and empty the queue */ - if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) { - __tty_buffer_flush(port); - clear_bit(TTYP_FLUSHPENDING, &port->iflags); - wake_up(&tty->read_wait); - break; - } else if (!count) + mutex_lock(&buf->lock); + + while (1) { + struct tty_buffer *head = buf->head; + int count; + + /* Ldisc or user is trying to gain exclusive access */ + if (atomic_read(&buf->priority)) + break; + + count = head->commit - head->read; + if (!count) { + if (head->next == NULL) break; + buf->head = head->next; + tty_buffer_free(port, head); + continue; } - clear_bit(TTYP_FLUSHING, &port->iflags); + + count = receive_buf(tty, head, count); + if (!count) + break; } - spin_unlock_irqrestore(&buf->lock, flags); + mutex_unlock(&buf->lock); tty_ldisc_deref(disc); } @@ -499,19 +501,13 @@ void tty_flush_to_ldisc(struct tty_struct *tty) * * In the event of the queue being busy for flipping the work will be * held off and retried later. - * - * Locking: tty buffer lock. Driver locks in low latency mode. */ void tty_flip_buffer_push(struct tty_port *port) { struct tty_bufhead *buf = &port->buf; - unsigned long flags; - spin_lock_irqsave(&buf->lock, flags); - if (buf->tail != NULL) - buf->tail->commit = buf->tail->used; - spin_unlock_irqrestore(&buf->lock, flags); + buf->tail->commit = buf->tail->used; if (port->low_latency) flush_to_ldisc(&buf->work); @@ -526,19 +522,18 @@ EXPORT_SYMBOL(tty_flip_buffer_push); * * Set up the initial state of the buffer management for a tty device. * Must be called before the other tty buffer functions are used. - * - * Locking: none */ void tty_buffer_init(struct tty_port *port) { struct tty_bufhead *buf = &port->buf; - spin_lock_init(&buf->lock); - buf->head = NULL; - buf->tail = NULL; + mutex_init(&buf->lock); + tty_buffer_reset(&buf->sentinel, 0); + buf->head = &buf->sentinel; + buf->tail = &buf->sentinel; init_llist_head(&buf->free); - buf->memory_used = 0; + atomic_set(&buf->memory_used, 0); + atomic_set(&buf->priority, 0); INIT_WORK(&buf->work, flush_to_ldisc); } -